The original route runs northward from just west of Union Station in downtown Toronto, ending just south of North Bay.

Access to Toronto is currently via the Bala Subdivision at Washago Junction, a short distance north of the remaining section's southern terminus, which is now used as a spur serving industries.

The Northern was purchased by the Grand Trunk Railway in 1888, whose bankruptcy in 1918 led to the line becoming part of the newly formed CNR in 1923.

This junction has been grade separated and has allowed increased commuter traffic on the line, including 15 minute service and weekend trains.

[3] On September 21 2019, the Canadian Railway Preservation and Restoration Association (CRPRA) expressed their interest in that section of the Newmarket Sub to operate a local tourism train.